1. Field of the Invention
The present invention relates to a wedge base bulb, and more particularly to a structure of a wedge base bulb utilized for a direction indicator lamp and a tail/stop lamp of an automobile or the like.
2. Description of the Background Art
A bulb utilized for a direction indicator lamp or a tail/stop lamp of an automobile has made the transition from a base-attached bulb 200 shown in FIG. 7 to a wedge base bulb 300 shown in FIG. 8 since the latter half of 1980""s, for the purpose of attaining lighter weight, automated assembling, reduced cost and so forth. Currently, wedge base bulb 300 is employed for most automobiles. For example, a direction-indicating lamp unit utilized for an automobile is constituted by a synthetic resin lamp lens colored with a warm color of amber, and a colorless and transparent wedge base bulb.
In recent years, however, more importance has been attached to design of automobiles, so that a direction-indicating lamp unit, in which the synthetic resin lamp lens is made colorless and transparent whereas the glass bulb itself is colored with the warm color of amber, has been employed.
An industrially utilized colored glass of a warm color tone such as red, amber, yellow or the like is processed by heat-melting a glass including a color-developing compound of CdS and CdSe or the like, or a color-developing element of Au, Cu or the like under an atmosphere where no such a color-developing element is oxidized (hereinafter referred to as reducing atmosphere) for a few minutes to a few hours in a predetermined temperature region (so-called colloid coloring). By making most use of these appropriate processing conditions, coloring of the bulb for an automobile is enabled.
When the base-attached bulb is employed for the direction-indicating bulb of an automobile, the glass bulb is manufactured by a manufacturing process described below to enable development of a desired color and chromaticity (amber). First, a molding section of a glass tube colored with CdSxe2x80x94CdSe colloid (coloring is insufficient in this state) is re-melted under the reducing atmosphere in a predetermined temperature region (in a range of the glass softening temperature to the glass softening temperature +100xc2x0 C. or lower). Subsequently, the melted glass tube is placed in a mold, and air is blown into the glass tube (or negative pressure is produced for suction in the mold) to expand the glass tube.
However, in a conventional method, when the wedge base bulb is employed for a direction indicating bulb of an automobile, one end of a glass tube colored by CdSxe2x80x94CdSe colloid (coloring is insufficient in this state) is melted under the reducing atmosphere and in a predetermined temperature region (in a range of the glass softening temperature to the glass softening temperature +100xc2x0 C. or lower) to form a hemispheric shape, and the other end is press-sealed under the reducing atmosphere and in a predetermined temperature region (in a range of the glass softening temperature to the glass softening temperature +100xc2x0 C. or lower) in a similar manner. Thus, a hemispheric head (portion A) and a press-sealed portion (portion C) of the glass bulb of a wedge base bulb 300 shown in FIG. 8 can develop a desired color. Whereas, a tubular body (portion B) is not re-melted under the reducing atmosphere and in a predetermined temperature region, resulting in unsatisfactory color development.
Further, the glass bulb of the wedge base bulb may be formed to have a standard wall thickness by a manufacturing process similar to that for the base-attached bulb, in which the glass tube colored by CdSxe2x80x94CdSe colloid (coloring is insufficient in this state) is re-melted under the reducing atmosphere in a predetermined temperature region (in a range of the glass softening temperature to the glass softening temperature +100xc2x0 C. or lower), is placed in a mold, and air is blown into the glass tube (or negative pressure is produced for suction in the mold), to expand the glass tube, and then the resulted tube is press-sealed. However, the press-sealed portion will have an insufficient thickness, since only a little glass material can be appropriated for the press-sealed portion.
If the glass bulb is to be manufactured by making the wall of a conventional glass tube thicker such that the wall thickness of the press-sealed portion would be a predetermined thickness, a longer processing time will be required. Further, an expensive colored glass is used, so that the wedge base bulb will be very expensive. Moreover, because of the thicker wall, desirable color, chromaticity and luminous flux may not be attainable.
With the technical background described above, the current state is such that the amber-colored direction indicating bulb must be selected from either the base-attached bulb which can be manufactured to have a relatively thin wall, or the wedge base bulb formed by coating paint on the surface of the colorless and transparent glass bulb.
However, if the base-attached bulb is employed, a socket must be changed from the one for the wedge base bulb used for most automobiles to the one for the base-attached bulb, which would be a negative factor in cost. Also, this would go against the current of the times toward the wedge-based bulbs for automobiles.
Furthermore, if the wedge base bulb of a conventional colorless and transparent glass bulb is employed and paint is coated on the surface of the glass bulb, it would be difficult to coat the surface without a risk of generating coating unevenness, pinholes or the like thereon, and also the paint may be discolored or stripped due to a raised temperature of the light when it is on.
An object of the present invention is to provide a wedge base bulb for solving the problems described above, which accommodates to a socket for the wedge base bulb and produces a predetermined color and chromaticity.
To achieve the object described above, a wedge base bulb according to the present invention includes a bulb body including a colored glass bulb, a filament housed in the colored glass bulb and a lead connected to the filament at a tip-end side thereof, the bulb body being press-sealed so as to expose a proximal-end side of the lead from the colored glass bulb; and a tubular insulation collar attached to cover a press-sealed portion of the bulb body. The colored glass bulb is formed by a process in that a molding section of the glass tube including a color-developing compound or a color-developing element is heat-melted under a reducing atmosphere and in a predetermined temperature region and thereafter the glass tube is placed in a mold and expanded in the mold, and also develops color with colloid generated by the heat-melting.
Thus, in the wedge base bulb according to the present invention, the colored glass bulb molded to have a thin wall and color-developed with colloid is employed and then a press-sealed portion with insufficient wall thickness is compensated by the insulation collar, to accommodate to a socket for the wedge base bulb of a predetermined shape. Further, the wedge base bulb developed to desired color and chromaticity can be attained at a low cost.
Preferably, the glass tube has a heat-melting temperature ranging from a softening temperature of the glass bulb to a glass softening temperature +100xc2x0 C. or lower. Further, the color-developing compound is preferably a compound selected from a group consisting of CdS, Cu2O, FeS, SbS2 and Sb2S3. Preferably, the color-developing compound is a mixture of CdS and CdSe. Further, the color-developing element is preferably an element selected from a group consisting of Cu, Ag, Au, S, Se and P. Preferably, an outer surface of the press-sealed portion and an inner surface of the insulation collar are respectively provided with engagement regions engaging with each other. Preferably, an inner surface of the insulation collar is provided with a ridge extending along an inserting direction of the press-sealed portion. Preferably, the ridge is provided in a number of four to twelve.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.